The present invention relates to moving sorbent filter devices, particularly moving sorbent filters designed to be used in air delivery fans.
Adsorbent air filters are conventionally formed of porous adsorbent media. The air is passed through the porous media which removes the gaseous based physical entrapment, absorption adsorption, or the like. The filter media can be particulate adsorbents such as activated carbon, silica gel, or activated aluminum or the like formed into a sheet or other form by particulate binders, adhesives, entrapment in a fibrous or other matrix or other means. The adsorbent media can be flat or formed into a three dimensional configuration. Pass through type filters will act on the entire airstream passed through the filter media with an associated pressure drop and filtration efficiency that is characteristic of the media, its level of loading and the airstream velocity and pressure. A problem with these filter medias is that they become loaded creating pressure drop increases.
Generally, most filters used are static with the air driven through the filter. However moving type filters have been proposed. Moving particle filters have been proposed, for example, to keep fresh filter media in the path of the airstream to be filtered as disclosed in U.S. Pat. No. 5,560,835 (driven slowly by drive rotor) or U.S. Pat. Nos. 4,038,058 and 3,898,066 (filter media driven by air impinging on rotor blades). These filters operate like conventional flow-through static filters and have the associated problem of pressure drop buildup over time. Flow through type filters have also been associated with faster moving devices such as rotating disk drives (U.S. Pat. No. 4,308,041), on an air inlet to a combine vent fan (U.S. Pat. No. 3,392,512), between fan blades on an air inlet fan for a turbine engine (U.S. Pat. No. 3,402,881), on a fume exhaust fan (U.S. Pat. No. 4,450,756), or in an air inlet to a building ventilation fan (U.S. Pat. No. 3,126,263). The proposed filters placed on a fan designed to circulate air (e.g., U.S. Pat. Nos. 3,402,881 and 4,450,756) have the filter media strategically placed to ensure that all the air passing through the system is passed through the filter media. In U.S. Pat. No. 3,402,881, the filter media 100 is woven between fan vanes 98 and sealed to prevent air from bypassing the filter media. This requires that the filter media be periodically cleaned. This cleaning is done by a complicated periodic backflow of air from the engine compressor or like source of high pressure air in the system. With U.S. Pat. No. 4,450,756, the filter must be periodically removed and cleaned or replaced. If the filter is not replaced when loaded, the pressure drop across the filter rises often to unacceptable levels, cutting off airflow. Although not desirable generally in certain filter applications this reduction in airflow is unacceptable.
It has been proposed in the art to use sorbents or sorbent filters with moving fans and the like. In U.S. Pat. No. 4,292,055, active chemical reagents such as activated manganese dioxide or other oxidizing agent are coated onto or impregnated into a rough surface material to allow for the cleaning of gaseous fluids passing over the moving surface of a rotor or other rotating surface. The "filtering" surface does not allow fluid to pass. It has also been proposed in U.S. Pat. No. 5,256,476 to mold adsorbent particles such as silica, zeolites or activated carbon into a variety of three-dimensional shapes using a blend of plastic particles and the adsorbents. As they are molded under pressure, there would be minimal permeability of the resulting article. U.S. Pat. No. 5,514,197 disclose a rotating paddle wheel with blades that are formed in part of woven activated carbon filaments. The device does not actively move air, rather is placed at the inlet of an air-purifying device.
With sorbent or particulate filters in automotive cabin applications, increases in pressure, due to filter media particle loading can drastically reduce airflow, which can result in dangerous window fogging. In automotive or furnace filter applications, the general approach has been to place a particle and/or sorbent filter at some location in the airstream (e.g., in the ducts) to intersect the entire airstream. The filter is generally very open to prevent undue increases in pressure drop, optionally with sorbent filters a particle filter can be used upstream to prevent filter clogging and increased pressure drop. Commercially the almost universal approach has been to place filters at various locations between the air inlet and air outlet in a vehicle or home heating and air conditioning system. An issue with these filters is they are often difficult to access unless they are located near the air inlet or outlet(s). However if the filter is located at or near an air inlet (which generally are easy to access) the filter only filters incoming air or recirculated air, but not both, unless multiple filters are used at the air inlet(s) for fresh air and the air inlet(s) for recirculated air. In a novel variant of this general approach, U.S. Pat. No. 5,683,478 proposes placing a static particle and/or sorbent filter inside a fan of the blower motor assembly intersecting the airstream immediately prior to the fan, as both recirculated and fresh air directed through the fan are filtered.
Ceiling fans have also been provided with filters. Generally, as discussed in WO 97/44624 (Crowhurst et al.), the filter media is provided on the outside surface of the fan blades. This patent application proposes placing a particulate or sorbent filter in the fan blade to allow air to pass through from a high pressure zone on the bottom of the fan blade to a low pressure zone on the top of the fan blade. The filter material can be sorbent or particulate filter materials. However, none is specifically disclosed. Other ceiling fans provide with particulate filters include U.S. Pat. No. 5,370,721 (placed on top of fan blade); U.S. Pat. No. 5,341,565 (cavity in fan blade provided with rigid filter elements); U.S. Pat. No. 4,889,543 (filter attached between fan blades); U.S. Pat. No. 4,840,650 (filter material of nonwoven fibers in frame secured to leading edge of fan blade); U.S. Pat. No. 4,753,573 (particulate filter adhered to surfaces of fan blade which filter could also have activated carbon impregnated into filter); and U.S. Pat. No. 4,676,721 (cover of woven material attached to fan blades). With ceiling fans of this sort, filtration is limited by the large volume of air moved. Low efficiency is offset by recirculation, which allows the fan to operate on the same air repeatedly unlike in a single pass housed system.
With single pass housed systems, air is passed through ducting or a housing or the like containing the air moving fan or the like. Unlike a ceiling fan, all the air must pass through the fan and the inlet and exit flow channels on either face of the fan. With this type of closed system, conventional flow through filter materials that are used function at very low pressure drops to ensure that the system, even if the filter is fully loaded with particulates, does not unacceptably reduce airflow. However, if the filter media is of the very low pressure drop type it generally is a low efficiency filter. Alternatively, it has been proposed that a certain portion of the airflow bypass the filter to ensure that pressure drop does not rise unacceptably during the lifetime of the filter. An air bypass of this type can eliminate the issue of unacceptably reduced airflow through the HVAC system due to a fully loaded filter but severely impacts filtration efficiency, particularly when filtering incoming air. Ideally, to ensure adequate airflow to an automotive cabin, the pressure drops of a filter in the HVAC system should show little or no pressure drop or reduced airflow over its lifetime, no matter how long it is in use. Similarily, home heating system filters should not significantly reduce airflow even when fully particle laden.